Topic 19: Thermodynamics

Question 1

Bond enthalpy

Answer 1

The amount of energy required to break one mole of the stated bond in the gas phase

Question 2

Born-Haber Cycle

Answer 2

Calculates the lattice enthalpy by applying Hess’s law and comparing the standard enthalpy change of formation of the ionic compound to values such as ionisation energy and electron affinity

Question 3

Covalent character

Answer 3

The partial sharing of electrons between atoms that have an ionic bond

Question 4

Enthalpy of atomisation

Answer 4

Enthalpy change when one mole of gaseous atoms is formed from the elements in its standard states. It is always endothermic

Question 5

Enthalpy of formation

Answer 5

Enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions

Question 6

Enthalpy of hydration

Answer 6

Enthalpy change when one mole of a gaseous ion is completely dissolved in water under standard conditions

Question 7

Enthalpy of lattice dissociation

Answer 7

Enthalpy change when one mole of a solid ionic compound is converted into its gaseous ions

Question 8

Enthalpy of lattice formation

Answer 8

Enthalpy change when one mole of solid ionic compound is formed from its gaseous ions

Question 9

Enthalpy of solution

Answer 9

Enthalpy change when one mole of ionic solid completely dissolves in water under standard conditions to form an infinitely dilute solution

Question 10

Entropy

Answer 10

A measure of the disorder of a system. The units are JK-1mol-1. On a molecular level gases –> liquids –> solids in order of disorder. A reaction that produces a greater number of molecules than the number of reactants –> positive entropy change –> exist more random arrangements of these molecules - system will become more disordered

Question 11

Feasible reaction

Answer 11

For a reaction to be feasible at a given temperature it must occur spontaneously. This means no extra energy is required for the reaction to occur

Question 12

First electron affinity

Answer 12

Enthalpy change when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Question 13

First ionisation energy

Answer 13

The energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

Question 14

Gibbs free-energy change

Answer 14

A measure of the feasibility of a chemical reaction

Question 15

Ionic character

Answer 15

the amount the electrons are shared between two atoms. Limited electron sharing corresponds with a higher percentage of ionic character